In the photoflash lamp art, it is a common practice to activate the lamp electrically from a low-voltage or a high-voltage source. Ordinarily, lamps utilizing a low-voltage source include a filament which bridges a pair of electrical conductors. This filament is heated in an amount sufficient to ignite a primer material which, in turn, ignites a combustible filamentary or shred material and provides the desired light output from the lamp.
The high-voltage type of photoflash lamp does not require the above-mentioned filament but rather relies upon a primer material which bridges a pair of electrical conductors. Upon application of a relatively high voltage, several hundred to several thousand volts, to the electrical conductors, the primer material is ignited and a combustible filamentary or shred material is activated to provide the desired light output.
In the constant search for improved light output and a reduced lamp size, it has been observed that the filamentary type lamp utilizing a low voltage source is inconsistent with the desired maximum light in a minimum space concept. Specifically, the mount structure required tends to undesirably reduce the space available within the flashlamp envelope which may be utilized to house light-producting material. Thus, the ratio of light attainable per unit space is undesirably limited.
An effort to overcome the above-described undesirable limitations is the utilization of a high-voltage electrical source. In this manner, the need for a filament is reduced and it becomes possible to rely on a layer of primer material bridging the electrical conductors as a source for igniting the combustible material within the lamp. Thus, the space for filament and filament supporting structures becomes available for utilization in providing light output.
However, one of the problems encountered when a primer material is employed as a bridge between a pair of electrical conductors is a condition which might be termed "Shred Shorting." Therein, the shred or combustible filamentary material utilized to provide light output comes in contact with the electrical conductor. As a result, the current passes through the shred material rather than the primer material and the primer material is, in effect, short-circuited. Thus, ignition of the primer material fails to take place and a flash failure results.
One of the known attempts to overcome the above-described "shred shorting" condition is described in U.S. Pat. No. 3,602,619. Therein, a glass tube, 19 or 21, is utilized to insulate the primer material from the shred material and thereby inhibit "shred shorting." However, it can be seen that the glass tube and mount structure is deleterious to a maximum utilization of available space for light producing capabilities.
Another known flashlamp configuration for reducing the tendency toward "shred shorting" is illustrated in U.S. Pat. No. 4,229,161. Herein, a mica disc is utilized to separate the primer and combustible materials. However, it may be noted that the disc and mount structure require space which would be better utilized as an area containing light producing materials.
Still another flashlamp configuration for maximizing light output per unit space is illustrated in the prior art embodiment of FIG. 1 of the drawings. Herein, a pair of electrical conductors 5 and 7 protrude through the seal 9 and into the inner volume 11 of a flashlamp envelope 13. A layer of primer material 15 bridges the electrical conductors 5 and 7 and combustible filamentary or shred material 17 is disposed within the envelope 13.
Although the above-described structure enhances the light output per unit space of the flashlamp, it was found that the electrical conductors 5 and 7 protruding into the envelope 13 tended to contact the shred material 17. As a result, the primer material 15 is undesirably short-circuited by the shred material 17 and flash failures result.